Level design is not that hard. Have a look at levels that you think are good. Either the original levels or other people's levels. Think about what makes a level good. Then think about what makes a level bad. It's just a matter of avoiding the common mistakes and making something original

I thought we needed this as nearly all of the help being handed out is on the technical side of affairs, and it's lead to a deficit in knowledge of how to make a hack that is appealing. Here's the result. Enjoy!

Okay, there's some things you should know before making a hack, and some things you should do before, while making, and releasing.


Quick note: making a hack is not easy. It will take quite a bit of time and effort, even to make a single hack. It's not something you can just throw out in five minutes, as it requires you to put in a fair wedge of brainpower. Therefore, if you don't have the capabilities to read this single post, I doubt you'll have the capabilities to make a proper hack. Now let's get on with it!


BEFORE:
Think about whether you want to edit the tileset. If you do, this is best done early on. It's a bad idea to completely start from scratch with these, as you can save yourself a lot of work by redoing it block by block, and keeping the blocks in their normal places. This way, all the blocks go together nicely, and if you abandon your hack, you can submit it to a community project. Another thing you might want to think about is how long a hack you're going to make. If you're going to make a full hack, it's a completely different game to making an individual level.

Individual level:
PLAN. An individual level needs plenty of effort put into it or it will look like a quick hack made by someone who doesn't put any effort in. This would be bad. However, with an individual level, you have loads more freedom. Choose the kind of level you want, and how many areas it needs. Then choose a fitting level, change anything needed (tileset, sprite sets, etc) and get to it!
NB: World 1-1 is probably the best as it is the first on the list and has three areas, but if you want another one, I'm not going to stop you.

Full hack:
Okay, you probably should plan, but that would be a pain. Just build the levels as they come to you, anyone with enough creativity can do this, just don't go crazy with platforms everywhere. With a full hack, obviously it's superior to an individual level as there's so much more, but in each level, you have a lot less freedom. This is for one simple reason. It looks really stupid if you go into World 1-1, an obvious grass level and end up underground, or in lava. It makes no sense, so please don't do it. (If you've already done it, just shuffle the levels around a bit til they all fit.) This is easy enough to do, as long as when you redesign the tilesets, you stick to the theme, and you don't change the tilesets in level unless you have to (or really really want to) and it still fits.


DURING:
First step is to delete all objects, sprites and entrances (not the starter/halfway ones if you don't want to). (You can delete the view and progress path too if you want too, but I always saw this as overkill.) Now start designing your level from scratch. Don't make a remake please, as these are copyright Nintendo, show no originality, and are old, like the levels in the original New Super Mario Bros. It's not really anything exciting, as we've seen it before. Here's a few notes regarding making your level.

1) DIFFICULTY
Try not to make it a walk in the park, or frustratingly hard. It's good to have a beta tester or two to see how hard it is for someone who doesn't know all the tricks you put in. It's not too hard to change the difficulty. We all know that to make something easier, just add more helpers and take away hinderers. To make something harder, add more hinderers and take away the helpers. What are the helpers and hinderers though? Easy. The helpers are the things that aid you (coins, 1-ups, power-ups), and the hinderers are the things that hurt you and slow you down (enemies, holes). Just adjust the balance until it's challenging, but doable.

2) THE TIME LIMIT
This is another point where your beta testers will come in handy. The only really good way to tell how long you're going to take to get through it is to test it. Let your beta testers loose on the level, and let them tell you if the time's too lenient or practically impossible. It's not too hard to tweak it a bit so you can get through it comfortably. Just remember to keep it to multiples of 100.

3) COINS
Standard coins should be all over the place. They should always mark out a good way to go, and are generally in groups of 2-5. Don't put some coins pointing towards death, as this is harsh, and if you make a jump and put coins over it, make sure they are actually gettable without the player dying.
Star coins are a whole different ball game. These need to be hidden, and be hard, but not impossible to find. Remember that a player should be able to find them without doing a nearly impossible jump after going through a certain patch of wall that is pass-through, because this is ridiculous. Hide them in unobvious and varied places too, as if you always hide them down the third pipe and to the left, this quickly becomes easy. Basically, not in open view, but still findable.

4) GENERAL STYLE TIPS
- Don't make it too 'tricky'. By this I don't mean too hard (although this is important), but not too many little tricks to get through the level. This may make you think you look cool, taking secret exits here, there and everywhere, but the general public won't want to have to watch you showing off before they can complete your level.
- Aesthetics are nice to stop your level looking dull. Just little things, like flowers or bushes as little decorations make it look just a bit more lively.
- Not too long, not too short. No-one wants a level to finish before they've really got into it, and no-one really wants to play a level that goes on so long it gets dull. About 5000 pixels is good, though this is a flexible number. Look at the Nintendo levels to see what they do.
- Don't forget to use the areas. In the levels that have different areas, you'll want to use the other areas for a bit of variation. It changes the mood a bit, as it is dissimilar to the rest of the level.
- Blind jumps generally make it considerably harder, and are frowned upon.
- Save regularly. Crashing happens.
So go ahead and start crafting your creation. You'll probably not find it too hard to make, if it is time consuming. Once you're on your way, it's time for the release.


RELEASING YOUR HACK
If you're going to release your hack, do not make a topic saying "Hi, I'm going to make a hack called Super Mario Revenge Bros 7. It's going to..." as people are unlikely to believe you with nothing to show for what you've said, and you'll look stupid if you can't or don't do something you said earlier. Wait til you have a fair bit done, and a couple of teaser trailers. If you're going to put some spoilers in, mark them as spoilers so people who want to work it out for themselves still can. It's better to only make topics about completed individual level hacks, of at least half-way done full hacks. It helps to set a release date, and don't make it too optimistic. If you want, you can release a teaser level from your hack when it's nearly complete, to raise interest for the release. Always distribute patches, as these are fully legit and a smaller file size. If you realise you left too much legroom in your release date, as long as it wasn't set for a special occasion, you can move around. As long as you give about a week's notice, people will only be happier you got it out before the release date. If, on the other hand, you realise you were too optimistic, change the release date at least a week before t was due, as a week is when people start getting excited.
Well, that's all you need to know (I think) on making a really nice hack that appeals to the people. Good luck, and have fun!